Fossil fuels have long been burned for the production of energy throughout the world. Unfortunately, such sources of energy (such as coal, lignite, fuel oil, peat, and other like materials) also invariably include many unwanted pollutants that are easily emitted therefrom during such a process. Included within this list of pollutants is mercury, a compound that has been known to cause a plethora of defects in animals. It has been a need within the fossil fuel industry to provide a cleaner manner of generating energy by reducing such emissions of pollutants, significantly mercury, from entering the atmosphere. Such a process is extremely difficult to achieve, for a number of reasons, without incurring large expenses. For instance, mercury removal may be provided through initial purification of the fossil fuel itself; however, such an alternative is nearly impossible to accomplish without impacting the energy source during such a step. Furthermore, completely capturing all emissions for further utilization is not possible due to the sheer volume of gases generated, the extreme heat exhibited by such emissions, and the lack of utility of the vast majority of such emissions in general. As such, the production of such fossil fuel emissions has been tempered through an allowance of a certain amount of pollutants within the atmosphere, coupled with the drive to reduce such emissions over time.
Furthermore, the most popular emissions reduction materials, being carbon-based, are very difficult to dispose of effectively. The resultant fly ash from a fossil fuel-burning smokestack (for example) will contain many different unwanted pollutants that are not permitted in many landfills and like locations. As such, recycling of such fly ash residue in end-use products deemed acceptable from a captured-pollutant perspective is a desirable outcome. With carbon-based filter media, however, such a result is not easy to accomplish. The ability to incorporate a carbon-based pollutant removal material in concrete is very troublesome as such a filter medium material is not compatible for stability purposes within such a product. Hence, there remains a need to develop a non-carbon-based filter medium that exhibits the desired ability to permit recycling of such materials.
Various possibilities have been provided within the fossil fuel emission reduction industry recently to that end. Currently, the most commonly used method for mercury reduction is ACI (activated carbon injection) into the flue stream of coal-fired power plant. Ample examples of ACI use and issues are known. Coal-fired combustion flue gas streams are of particular concern because their composition includes trace amounts of acid gases, including SO2 and SO3, NO and NO2, and HCl, flue gas components that have deleterious effect on activated carbons. Powdered activated carbon has shown effectiveness as part of a Hg+2 capture mechanism; unfortunately, this ionic species is not the only mercury type present within typical flue gases. Such a removal product is not as effective for the more prevalent elemental mercury pollutant. There have been efforts to enhance the Hg0 trapping efficiency of powdered activated carbon by incorporating bromines therein; however, the environmental impact of such components is still debated, not to mention the higher costs associated with fly ash reuse make this approach suspect to the degree that a more desirable alternative is needed.
Alternatives for powder activated carbon were attempted at times but usually failed to remove mercury as efficiently. Of greatest note are U.S. Pat. Nos. 6,719,828 and 7,048,781, dedicated to metal sulfide moieties attached to ion-exchange sites on impregnated silicates. The '828 patent describes a preparation of layered sorbents such as clays with metal sulfide between the clay layers and methods for their preparation. The method used to prepare the layered sorbents is based on an ion exchange process, which limits the selection of substrates to only those having high ion exchange capacity. In addition, ion exchange is time-consuming and involves several wet process steps, which significantly impairs the reproducibility, performance, scalability, equipment requirements, and cost of the sorbent. The '781 patent describes phyllosilicate substrates (most notably, vermiculite and montmorillonite), and require an initial metal treatment to create such ion-exchange locations thereon the surface. From there, a polyvalent metal sulfide is produced through an ion-exchange process on the surface, thus permitting the sulfide moiety to be present at a location wherein reaction with a fixed-bed filtration medium including such a material will result in capture of mercury ions with the sulfide moieties. Such compounds appear to be successful for their intended purpose; however, there is complexity involved in the ion-exchange mechanism that makes production of such materials relatively difficult to accomplish and suspect in reliability as a result.
There is thus a need for the provision of a simpler method to provide an effective non-carbon-based mercury flue gas emission removal material for the fossil fuel industry. This invention has been determined to fill this void.